This invention relates to monitoring the condition of a component in a heating, ventilating and air conditioning unit and, in particular, to monitoring the condition of an air filter.
A heating, ventilating and air conditioning unit (HVAC unit) typically includes a filter which filters the air being drawn into the unit. The filter will lose its ability to properly filter the incoming air over time due to the build up of airborne particles captured by the filter. It is usually difficult to visually inspect the condition of the filter for such a build up without dismantling the unit itself. In order to provide an automatic indication of air filter condition that does not require visual inspection, systems have been developed that track the accumulated run time of a fan that draws air into the unit. When the accumulated run time exceeds a certain limit, a warning is given that the filter needs to be replaced. This way of detecting a dirty filter is not all that accurate because it does not take into account the quality of the air being processed through the unit. In this regard, relatively clean air will allow for a longer filter lifetime than if lower quality air is being processed through the unit. What is needed is a more accurate measurement of the condition of the filter itself.
The present invention provides an HVAC unit with an electronic system for detecting the condition of the filter in the unit regardless of the environment in which the unit is operating in. The electronic system includes a microprocessor control, which defines at least one command for a driver circuit for the motor of the fan producing airflow through the filter. The command to the driver circuit is preferably associated with a desired run speed for the fan. The computer control is operative to thereafter compute speed of the fan following issuance of the command to the motor drive circuit. This computed speed is compared to a predetermined fan speed that will occur when the filter is dirty. The electronic system is operative to generate a warning in the event that the computed fan speed does not compare favorably with the predetermined fan speed.
In a preferred embodiment, the computer control has the ability to issue more than one command to the driver circuit for the fan motor. Each such command is associated with a stored fan speed that can be used to determine whether a computed fan speed indicates a dirty filter. In a further preferred embodiment, the electronic system is operative to learn and define the one or more operating speeds indicative of a dirty filter condition for the particular unit. These values are stored to for use by the electronic system in determining whether a clean or dirty filter is present in the unit.